1. Field of the Invention
The present invention relates to systems and methods used in radiation imaging; and more particularly, to collimators utilized in cooperation with radiation detectors that permit only desired radiation to strike the detector thereby producing a more accurate image-of-interest, typically of an internal portion of a patient when medical and diagnostic applications are considered.
2. Description of the Background Art
In conventional radiation imaging arrangements, collimators are used in a wide variety of equipment in which it is desired to permit only beams of radiation emanating along a particular path to pass a selected point or plane. Collimators are frequently used in radiation imagers to ensure that only radiation beams passing along a direct path from the known radiation source strike the detector thereby minimizing detection of beams of scattered or secondary radiation.
Particularly in radiation imagers used for medical diagnostic analysis or for non-destructive evaluation procedures, it is important that only radiation emanating from a known source and passing along a direct path from that source be detected and processed by the imaging equipment. If the detector is struck by undesired radiation such as that passing along non-direct paths to the detector, performance of the imaging system can be degraded.
Collimators are positioned to substantially absorb the undesired radiation before it reaches the detector. The collimator includes (or is manufactured from) a relatively high atomic number material and the collimator is positioned so that undesired radiation strikes the body of the collimator and is absorbed before being able to strike the detector. In a typical detector system the collimator includes barriers associated with the detector and located in the direction of the radiation source. An example exists in radiation imaging systems used for medical diagnosis which use a small point source of radiation to expose the patient under examination. The radiation passes through the patient and strikes a radiation detector that is oppositely positioned.
Another diagnostic technology that incorporates collimators is the gamma camera typically utilized in Single Photon Emission Computed Tomography (SPECT) scanning, which is a nuclear medicine procedure in which gamma camera(s) have traditionally rotated around the patient taking pictures from many angles. From these images, a computer is employed to form a tomographic (cross-sectional) image of the internal area-of-interest within the patient using a calculation process that is similar to that used in X-ray Computed Tomography (CT) and in Positron Emission computed Tomography (PET).
In the instance of SPECT scanning, a subject (patient) is infused with a radioactive substance that emits gamma rays. Conventionally, a gamma camera includes a transducer to receive the gamma rays and record an image therefrom. In order for the image to be a true representation of the subject being investigated, a collimator having collimating apertures is positioned between the transducer and the subject to screen out all of the gamma rays except those directed along a straight line through the collimating apertures between a particular part of the subject and a corresponding particular part of the transducer. Traditionally, the collimator is made of a radiation opaque material such as lead, and collimating apertures have been formed therein by various means such as drilling, casting, or lamination of corrugated strips of lead foil.
In conventional SPECT system designs, the gamma cameras have been supported on gantries that rotate the camera heads through a specific angular range around the patient, usually covering one hundred eighty or three hundred and sixty degrees. One drawback associated with this requirement however, is that such gantry systems are relatively expensive subsystems of the diagnostic tool because they must be capable of providing rapid rotation is of the large and heavy camera heads through very precise orbits about the patient. As a result, the object of the present invention is to accommodate the use of lower cost, simplified gantries, without sacrificing image quality, or driving the cost of related subsystems higher.